feat(bootkernel): merge into regular kernel

This merges the bootkernel into the coreos-kernel. The reason we are
doing this is because on Xen, today, we don't have kexec so we need to
have a full kernel in this case.

This also updates bootengine so that it has the new logic to handle a
non-working kexec.
fix(bootengine): don't use host-only on dracut

host-only means that we don't include all of the modules that the kernel
provides. Only the ones that are needed for this machine. This won't
work since we rely on all of the modules since we don't have the
bootkernel anymore.
feat(sys-kernel/coreos-kernel): use bootengine

move the bootengine to coreos-kernel and delete the boot kernel config.
Merge pull request #102 from philips/bootengine-bump

feat(bootkernel): merge into regular kernel